Poor Interfacial Properties Research Articles

Improved Cycling Performance of Lithium–Sulfur Cell through Supramolecular Interactions

Commercialization of lithium–sulfur batteries is plagued by poor electronic conductivity of elemental sulfur, shuttling of polysulfides, and poor interfacial properties of lithium metal anodes with nonaqueous electrolytes. Although numerous attempts have been made to alleviate such challenges, trapping of polysulfides within sulfur composite cathodes appears as an efficient way to improve the cycling performance of Li–S cells. In the present work, naphthyl viologen was successfully synthesized and incorporated in a sulfur cathode in order to enhance the electrochemical performance of Li–S cells. Charge–discharge studies revealed that the viologen-added Li–S cell delivered higher discharge capacity than the unladen one. The enhanced performance of viologen-laden sulfur cathode was attributed to the electrostatic interaction between polysulfide and viologen, which was further substantiated by UV–vis spectroscopy.

High-Performance Graphene-Based Natural Fiber Composites.

Natural fiber composites are attracting significant interest due to their potential for replacing synthetic composites at lower cost with improved environmental sustainability. However, natural fiber composites suffer from poor mechanical and interfacial properties. Here, we report coating of graphene oxide (GO) and graphene flakes (G) onto natural jute fibers to improve mechanical and interfacial properties. The coating of graphene materials onto jute fibers enhanced interfacial shear strength by ∼236% and tensile strength by ∼96% more than untreated fibers by forming either bonding (GO) or mechanical interlocking (G) between fibers and graphene-based flakes. This could lead to manufacturing of high-performance and environmental friendly natural fiber composites that can potentially replace synthetic composites in numerous applications, such as the automotive industry, naval vessels, household products, and even in the aerospace industry.

Effect of “Z” factor for strength of interphase layers on the tensile strength of polymer nanocomposites

The influences of “Z” factor for the strength of interphase layers on the tensile strength of polymer nanocomposites and various interphase properties are explained applying three approaches including developed Leidner‐Woodhams, Pukanszky, and Callister‐Rethwisch models. All models and equations for interphase parameters are developed based on a multi‐layered interphase in different polymer nanocomposites. The calculations reveal that the role of “Z” factor is highlighted when much volume fraction of nanofiller ( ) is used attributed to the high probability of nanoparticles agglomeration and poor interfacial properties in this condition. However, both “ ” and “Z” parameters positively affect the tensile strength. Additionally, the highest values of interphase properties including “B” in Pukanszky and “s” in Callister‐Rethwisch models are achieved by the high levels of nanofiller strength and “Z” factor. POLYM. COMPOS., 40:1117–1122, 2019. © 2018 Society of Plastics Engineers

Electrode-Electrolyte Interfaces in Lithium-Sulfur Batteries with Liquid or Inorganic Solid Electrolytes.

Electrode-electrolyte interfacial properties play a vital role in the cycling performance of lithium-sulfur (Li-S) batteries. The issues at an electrode-electrolyte interface include electrochemical and chemical reactions occurring at the interface, formation mechanism of interfacial layers, compositional/structural characteristics of the interfacial layers, ionic transport across the interface, and thermodynamic and kinetic behaviors at the interface. Understanding the above critical issues is paramount for the development of strategies to enhance the overall performance of Li-S batteries. Liquid electrolytes commonly used in Li-S batteries bear resemblance to those employed in traditional lithium-ion batteries, which are generally composed of a lithium salt dissolved in a solvent matrix. However, due to a series of unique features associated with sulfur or polysulfides, ether-based solvents are generally employed in Li-S batteries rather than simply adopting the carbonate-type solvents that are generally used in the traditional Li+-ion batteries. In addition, the electrolytes of Li-S batteries usually comprise an important additive, LiNO3. The unique electrolyte components of Li-S batteries do not allow us to directly take the interfacial theories of the traditional Li+-ion batteries and apply them to Li-S batteries. On the other hand, during charging/discharging a Li-S battery, the dissolved polysulfide species migrate through the battery separator and react with the Li anode, which magnifies the complexity of the interfacial problems of Li-S batteries. However, current Li-S battery development paths have primarily been energized by advances in sulfur cathodes. Insight into the electrode-electrolyte interfacial behaviors has relatively been overshadowed. In this Account, we first examine the state-of-the-art contributions in understanding the solid-electrolyte interphase (SEI) formed on the Li-metal anode and sulfur cathode in conventional liquid-electrolyte Li-S batteries and how the resulting chemical and physical properties of the SEI affect the overall battery performance. A few strategies recently proposed for improving the stability of SEI are briefly summarized. Solid Li+-ion conductive electrolytes have been attempted for the development of Li-S batteries to eliminate the polysulfide shuttle issues. One approach is based on a concept of "all-solid-state Li-S battery," in which all the cell components are in the solid state. Another approach is based on a "hybrid-electrolyte Li-S battery" concept, in which the solid electrolyte plays roles both as a Li+-ion conductor for the electrochemical reaction and as a separator to prevent polysulfide shuttle. However, these endeavors with the solid electrolyte are not able to provide an overall satisfactory cell performance. In addition to the low ionic conductivity of solid-state electrolytes, a critical issue lies in the poor interfacial properties between the electrode and the solid electrolyte. This Account provides a survey of the relevant research progress in understanding and manipulating the interfaces of electrode and solid electrolytes in both the "all-solid-state Li-S batteries" and the "hybrid-electrolyte Li-S batteries". A recently proposed "semi-solid-state Li-S battery" concept is also briefly discussed. Finally, future research and development directions in all the above areas are suggested.

Controlling charge balance using non-conjugated polymer interlayer in quantum dot light-emitting diodes

The balance of electron–hole charge carriers in quantum dot (QD) light-emitting diodes (QLEDs) is an important factor to achieve high efficiency. However, poor interfacial properties between QDs and their adjacent layers are likely to deteriorate the electron–hole charge balance, resulting in the poor performance of a QLED. In this paper, we report an enhanced efficiency in red-emitting inverted QLEDs by modifying the interface properties between QDs and ZnO electron transport layer (ETL) using a thin layer of non-conjugated polymer, poly(4-vinylpyridine) (PVPy). Based on the precise control of the electrical properties with PVPy, the maximum efficiency of the QLED is enhanced by 30% compared to the device without a PVPy layer. In particular, the efficiency at low current density region is significantly increased. We investigate the effect of the PVPy interlayer on the performance of QLEDs and find that this thin layer not only shifts the energy levels of the underlying ZnO ETL, but also effectively blocks the leakage current at the ETL/QD interface.

Better performing composite cathode encompassing graphene and magnesium aluminate for Li–S batteries

The issues such as low ionic conductivity of sulfur, shuttling of polysulfide intermediates and poor interfacial properties of lithium metal anode with electrolytes hamper lithium–sulfur batteries from commercialization. In order to conquer these issues, numerous attempts have been made by researchers across the world. Herein we introduce a novel ternary composite electrode composed of sulfur, graphene, and magnesium aluminate (MgAl2O4). Synergistically, each component functions for a specific purpose: the added graphene sheets facilitate for fast electron transfer while MgAl2O4 provides strong binding sites for trapping polysulfide intermediates. The sulfur active material which resides in this ternary mixture involves in the electrochemical reactions and delivers energy. With this unique architecture the Li–S cell delivered a specific discharge capacity of 1394, 800, 492 and 117 mAhg−1 at 0.1, 1, 2 and 5C-rate respectively on its first cycle. The charge–discharge characteristics are found to be better than earlier reports with metal–organic frame work as additive.

Addition-cure, room temperature vulcanizing silicone elastomer based syntactic foams with glass and ceramic microballoons

Syntactic foams based on addition cure, room temperature vulcanizing silicone elastomer with two types of microballoons, viz. glass and ceramic, were processed and characterized. The effect of microballoon concentration (varied from 0 to 30 wt%) on the physical, mechanical, thermal, thermo-physical and ablative properties of the foams was investigated. Syntactic foams with glass microballoon (GM) possessed lower density and higher void content compared to those with ceramic microballoon (CM). The specific tensile strength and elastic modulus showed significant improvement; particularly for 20% GM filled system due to good interfacial bonding with silicone matrix. For CM syntactic foam, most of the mechanical properties showed a decline with increase in CM content because of poor interfacial properties. The trend in mechanical properties was corroborated by the microstructure evaluation through scanning electron microscopic (SEM) analyses. The thermo-physical properties such as specific heat, thermal conductivity, thermal diffusivity and co-efficient of thermal expansion showed variations with the type and content of microballoon. Thermo-gravimetric analysis (TGA) showed accelerated thermal decomposition for GM filled system; whereas, CM filled system preserved the thermal stability of silicone along with increase in char residue. Ablative evaluation showed high heat of ablation for GM filled system compared to CM based syntactic foam. The study reveals that syntactic foams based on silicone elastomer with low density and enhanced mechanical properties, suitable for critical weight-sensitive applications, can be formulated with microballoon inclusion. Selection of the appropriate type and concentration of microballoon is crucial in realizing the syntactic foams useful for the intended application.

Solid Polymer Electrolyte Embedded with Ionic Liquid for Lithium-Ion Battery Operating at Ambient Temperature

The application of lithium-ion battery (LIB) is expanding from small electrical devices to electrical vehicles, which are required high energy, power and safety. Energy and power density were improved by developing cathode and anode. However, there are huge potential safety hazards when commercialized LIB employing organic solvent is applied electrical vehicles. The flammable organic solvents are considered the source of thermal runaway reaction of LIB. The solution to these problems is to replace the liquid electrolyte with solvent-free solid electrolyte for high safety and stability. Solid polymer electrolytes (SPEs) have been studied for potential use in lithium-ion batteries over the four decades.[1] They are composed of Li-salts dissolved in solid, coordinating polymers, such as poly (ethylene oxide) (PEO). However, Li+-conducting SPEs show poor ionic conductivity and interfacial properties. In the case of PEO, below 65 oC, ionic conductivity decreases dramatically as a result of crystallization, which severely restricts ion transport.[2] Thus, most PEO-based SPEs are not suitable for the electrical device which operating at ambient temperature. In this study, we made the high-performance SPEs for lithium ion batteries operating at room temperature. Furthermore, these electrolytes have good compatibility with electrodes by using direct casting on electrode. The electrolytes are composed of cross-linked polymer, lithium salts (Bis(trifluoromethane)sulfonimide lithium salt, LiTFSI) and ionic liquid (1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, EMITFSI). The cross-linked polymer can be prepared by reacting polyethylene glycol and 3-glycidoxypropyltrimethoxysilane. EMITFSI are selected for high ion mobility. The addition of ionic liquids cause the increase of ionic conductivity due to the enhancement of ion dissociation and improvement of ion mobility. Electrochemical impedance spectroscopy (EIS) and galvanostatic charging/discharging tests were performed with lithium iron phosphate (LiFePO4)/SPE/Li foil cells at the room temperature. The bulk resistance was decreased according to the amount EMITFSI whose value from 698.5 Ω to 105.3 Ω. Also, charge transfer resistances were decreased from 2507.4 Ω to 560 Ω. These results show that EMITFSI can enhance the ion conductivity. With increasing amount of EMITFSI, specific capacities were increased. This is mainly due to an increase of the lithium ion mobility when EMITFSI was increasing. The specific capacity of prepared cell with EMITFSI was 75.815 mAh/g and 16.538 mAh/g at 0.1C, 0.5 C respectively. The specific capacity of LiFePO4/SPE/Li Cell using SPE without ionic liquid was 15 mAh/g at 0.1 C. And capacities were recovered after high current rate charging/discharging test. Therefore, we believe that suggested SPEs act as a stepping stone to the realization of high-performance all-solid lithium-ion batteries operating at room temperature. [1] D.E. Fenton, J.M. Parker, P.V. Wright, Polymer 14 (1973) 589 [2] K.P. Barteau, M. Wolffs, N.A. Lynd, G.H. Fredrickson, E.J. Kramer, C.J. Hawker, Macromolecules 46 (2013) 8988-8994. Figure 1

Interfacial Properties of Saponin Extracts and Their Impact on Foam Characteristics

Saponins from various botanical origins highly differ in molecular structure. Little is known of the influence of structural differences between the different saponins on interfacial tension, short-term adsorption and foam properties at the air-water interface (a/w). In this study five triterpenoid saponins, with three of these being monodesmosidic and two bidesmosidic as well as one steroid saponin, were analyzed. Interfacial tension isotherms were measured using a tensiometer with a Wilhelmy plate and were fitted using the modified Frumkin model. For characterization of the short-term adsorption at the a/w-interface, two-fluid needle experiments were performed. Foaming, foam stability and foam structure were analyzed using a foaming device. A new method for semi-quantitative analysis of different foam structures was established. Additionally the impact of pH and ionic strength (addition of NaCl) on interfacial tension and foam properties were determined. The short-term adsorption of all saponins was limited by an additional barrier and was not diffusion-limited. Extracts from Quillaja saponaria Molina (QS), Gypsophila (GYP), Camellia oleifera Abel (TS) and Aesculus hippocastanum (ESC) lowered the interfacial tension to 37–42 mN/m and produced stable foams. The steroid saponin from Tribulus terrestris (TT) and the monodesmosidic saponin from Glycyrrhiza glabra (GA) had only poor interfacial and foam properties. Foams made from QS and GYP were only little affected by changes in pH and ionic strength. A reduction of the pH from 5 to 3 increased stability of foams made from GA significantly. Foams made from ESC and TS were negatively affected by increasing ionic strength.

Interlaminar toughening in flax fiber-reinforced composites interleaved with carbon nanotube buckypaper

Natural fiber-reinforced composites have advantages such as light weight, unique mechanical properties, good sound absorption, and heat isolation performances. However, low interlaminar properties of natural fiber-reinforced composite laminates caused by the poor interfacial properties between natural fibers and polymeric matrices have become one of the main obstacles for their applications. In this study, carbon nanotube buckypaper interleaf, which is network structures formed by carbon nanotubes, has been developed to utilize their potential for increasing interlaminar properties of flax fiber-reinforced composites. Synergistic effects between the buckypaper and the hierarchical structure of flax fibers on the interlaminar fracture toughness were investigated. The results obtained from double cantilever beam test indicated that the interlaminar fracture toughness of the composites was significantly improved with the addition of buckypaper. Fractured surfaces of the composites were observed with the aid of scanning electron microscopy. Improved interlocking between the flax fiber and the matrix by carbon nanotubes strengthened the interlaminar interfacial bonding, resulting in fiber fibrillation and matrix toughening. Improved impact performances also proved these mechanisms. Additionally, tensile tests confirmed that the introduction of buckypaper interleaves had no influence on the fiber-dominated in-plane properties.

The electrochemistry of lithium in ionic liquid/organic diluent mixtures

The electrochemistry of lithium is investigated in a number of electrolytes that consist of a lithium salt dissolved in a combined ionic liquid-organic diluent medium. We find that ethylene carbonate and vinylene carbonate improve electrochemical behaviour, while toluene and tetrahydrofuran are less promising.We also present insights into the electrode passivation caused by these diluents in an ionic liquid electrolyte during lithium cycling. We observe that during lithium cycling those electrolytes with carbonate based diluents are the most able to utilise their previously reported improved lithium ion diffusivities. Conversely, tetrahydrofuran, the most promising diluent of those studied in terms of its known ability to increase lithium ion diffusivity is found not to be as advantageous as a diluent. It appears that the poor electrochemical interfacial properties of the tetrahydrofuran electrolyte prevented the realisation of the benefits of the high solution lithium ion diffusivity.

Investigation of the Electrochemical Properties of Polymer–LiX–Ionic Liquid Ternary Systems

The electrochemical properties of ternary systems that consist of a polymer, a lithium salt, and an ionic liquid that shares the same anion (TFSI, bis(trifluoromethansulfonyl)imide) are reported and compared. The investigation involved two different polymers (PVdF-HFP and PTFE) that were selected because of their common use in lithium-based electrochemical devices. It was found that PVdF-HFP swelled by the ionic liquid used in the work while porous PTFE remained inert. The ternary electrolytes showed interesting ionic conductivities. However, the presence of fluorinated polymers resulted in poor interfacial properties with lithium metal electrodes.

Effect of Water Absorption Rates on Fracture Toughness of Sisal Textile Fiber Reinforced Composites

Using natural fibers that are inexpensive, lightweight and biodegradable, as the reinforcement for composites is difficult due to their poor interfacial properties between hydrophilic fiber and hydrophobic polymer matrices. It is necessary to evaluate fracture toughness of natural fiber reinforced composites according to water absorption rates to improve mechanical performance of those. In this study, compact tension fracture test was conducted to evaluate fracture toughness with the various specimens. The value of fracture toughness has the tendency to decrease as water absorption rate increases. And different surface treatment methods and different polymer matrices have influence on the value of fracture toughness.

Physical and electrical properties of reactive molecular-beam-deposited aluminum nitride in metal-oxide-silicon structures

We report on the physical and electrical properties of AlN as grown by reactive-atomic-beam deposition under various growth and anneal conditions. The physical characterization shows that AlN grown on hydrogen terminated (HF-last) Si has a thin layer of Si3N4 at the interface while growth of AlN on SiO2 or Al2O3 suffers from nucleation problems. The AlN on HF-last Si, grown and annealed at 650 °C, shows high interfacial quality and four to five orders of magnitude lower leakage current as compared to SiO2. In contrast, poor interfacial properties and leakage current are reported for the AlN grown on SiO2 or Al2O3. The relative permittivity of the AlN is found to be close to 18 and the equivalent thickness of the interfacial layer is approximately 6 Å. The effective electron mobility in Al-gated N-channel metal-oxide-silicon field-effect transistors with a 22 Å thick AlN layer peaks at ∼130 cm2/V s. The relatively low mobility is attributed to a combination of high concentration of fixed charge (>5×1012 cm−2) and charge trapping.

Adsorption dynamics and interfacial properties of α-lactalbumin in native and molten globule state conformation at air–water interface

The effect of conformation of α-lactalbumin on the dynamics of adsorption as well as on the properties of adsorbed layer at air–water interface were investigated. The surface hydrophobicity of molten globule conformation of α-lactalbumin (prepared by lowering pH to 2) was found to increase by 15-fold compared to the protein in its native form (pH 7) with increased flexibility as evidenced by a much smaller hysteresis area of spread surface pressure isotherms. This higher surface hydrophobicity resulted in (i) higher surface activity of α-lactalbumin in its molten globule conformation compared to the native form inspite of a much higher electrical energy barrier due to much higher net charge and (ii) diffusion controlled adsorption for much longer times and surface pressures than the native form. The diffusion coefficient of α-lactalbumin in molten globule state was lower than that for native form (2.22×10 −10 m 2 s −1 vs 4.65×10 −10 m 2 s −1) and increased for the former at higher ionic strength. The area per molecule during the dynamics of adsorption was found to be the same at a fixed surface pressure for both the conformations and lower than the corresponding value for fully denatured protein thus indicating that α-lactalbumin does not fully unfold at the interface in both the conformations. Even though α-lactalbumin adsorbed much more in its molten globule conformation, it gave poor interfacial rheological properties compared to the native form. Ionic strength did not influence the relationship between the interfacial elasticity and surface concentration for both the conformations.

Water sorption characteristics of epoxy resin-UHMPE fibers composites

Specimens of epoxy resin reinforced with ultrahigh-modulus polyethylene (UHMPE) fibers were immersed in water, and their swelling characteristics were recorded at various temperatures. In addition to an estimation of the response of those composite, the above study aimed at the exploration of the role of the fiber–matrix interface on the water sorption. Therefore, specimens containing original, calendered, and corona-treated fibers were tested. UHMPE fibers were found to limit the extent of sorption due to the nonhydrophilic character of polyethylene. However, specimens with poor interfacial properties, such as those with the original, untreated fibers, showed enhanced sorption since their surface area is drastically increased. As expected, the raise of temperature has a positive contribution to water sorption, and, furthermore, it seemed to affect the interface between epoxy and calendered fibers. On the other hand, the increase of filler volume fraction leads to a decrease in the amount of water uptake. The water transport in the neat epoxy resin specimens is rather diffusion-controlled, and this behavior was also recorded for the composite specimens reinforced with original UHMPE, which presented the maximum absorption. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 747–755, 1998

Liquid phase epitaxial growth of AlGaSb

Optimum conditions for the liquid phase epitaxial growth of AlGaSb and for the heat treatment of substrates were investigated. The high-temperature heat treatment of GaSb substrates prior to growth was found to damage the surface of the substrates, resulting in poor interfacial properties and formation of Ga inclusions. A “Dipped and Double Substrate” method is proposed to improve this situation. By this method, AlGaSb with good interfacial properties can be grown with good reproducibility. The optimum bakeout condition of the melt was found to be 24 h at 700°C. Photoluminescence spectra suggest that the residual acceptors are not only due to antimony vacancies but also due to such residual impurities as silicon. From laser Raman spectra, LO phonons are shown to couple with plasmons in AlGaSb when the background carrier concentration is as high as 10 17/cm 3.